Safety improvements in cam-and-spring operated impact tool



Filed Aug. 15, 1968 May 26, 1970 w. COIFFMAN-I ETAL 3,513,918

SAEETY IMPROVEMENTS IN CAM-AND-SPRING OPERATED IMPACT TOOL 3 Sheets-Sheet 1 KENNETH W. COFFMAN JOHN W. STEVENS RUPERT D. JONES 1 INVENTORS ATTORNEY May 26, 1970 K. w. COFFMAN ET AL 3,513,918

SAEETY IMPROVEMENTS IN CAM-AND-SPRING OPERATED IMPACT TOOL Filed Aug. 15, 1968 3 Sheets-Sheet 2 23, NW i II III! i|||| L l---' as 24 @3153 I as 46 '27.

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SAEETY IMPROVEMENTS IN CAM-AND-SPRING OPERATED IMPACT TOOL Filed Aug. 15, 1968 3 Sheets-Sheet :5

22 15 FIGURE 4 KENNETH W. COF'FMAN I JOHN W. STEVENS RUPERT D. JONES 1N VEN TORfi BY @34 M, 9)

ATTORNEY FIGURE 6 United States Patent 3,513,918 SAFETY IMPROVEMENTS IN CAM-AND-SPRING OPERATED IMPACT TOOL Kenneth W. Cofiman, John W. Stevens, and Rupert D.

Jones, Houston, Tex., assignors to Hughes Tool Company, Houston, Tex., a corporation of Delaware Filed Aug. 15, 1968, Ser. No. 752,901 Int. Cl. B25d 11/04 US. Cl. 173-119 4 Claims ABSTRACT OF THE DISCLOSURE A construction to reduce the hazard inherent in a power spring which is always at least partially compressed during every phase of operation of an assembled impact tool of the type wherein a rotating shaft which supports a pair of cam rollers causes such rollers to roll over an annular cam. The cam is thereby caused to reciprocate axially, alternately compressing the spring and suddenly releasing it as the rollers pass over the high shoulder of the cam surface. The released power spring propels the cam member and depending striker into forceful contact with a working tool.

The safety construction takes the form of a guide ring secured to the bottom end of the upper part of the split housing of the tool, this upper housing part having a closure at the top in contact with the upper end of the power spring. A pair of guide bearings are supported on studs secured to the guide ring and project radially inwardly into vertical slots in the striker which register with blind slots or pockets in the cam member. The slots serve to restrain the cam-striker from twisting, and the pockets define a stop to downward movement. Before assembling the lower housing to, the upper, the guide ring is secured to the upper housing with a pair of extra long safety bolts which are threaded through tapped openings in the upper housing and project above its lowermost, flanged end. The extra length is chosen so that the power spring can be compressed from its free length in assembly without the use of a press or vise.

The present invention lies in the field of impact or percussion tools, in which a hammer or striker reciprocates within a framework or housing and delivers a rapid succession of impacts to a working tool slidably secured to the lower end of the housing. More particularly, it concerns percussion tools of the type wherein the striker is integrated with a cam and the combination cam-andstriker is reciprocated axially to alternately compress a power spring and then release such spring. The released spring then becomes the acting force which rapidly projects the cam and striker toward the working tool to deliver a high energy blow to the tool.

Impact tools as thus generally constructed are disclosed in the US. patents issued in 1965 and 1967 to Jack A. Roll, 3,186,498 and 3,302,732, and it is to be understood that the invention herein is an improvement over the impact tools disclosed in such patents. The present invention has little to do with the principal contributions disclosed and claimed in the Roll patents, either the special shape of the cam in 498 or the special mountings of the cam rollers and their transport shaft in 732, but it is also to be understood that the impact tool described herein may utilize fully the R011 inventions of such patents.

SHORT DESCRIPTION OF INVENTION One particular area of improvement is in safety, as the spring powering such an assembled impact tool is always under at least partial compression, and accidents can occur in assembly or disassembly, particularly if certain parts are broken. The structure of the present invention adds a safety feature considerably reducing the probability of such accidents. This safety feature also makes it possible to assemble and disassemble the tool without using a special tool such as a press to compress the power spring, or to releae it gradually in disassembly.

This safety feature makes use of the fact that the housing for the working parts of the tool is divided into an upper housing and a lower housing, the two housings being connected together with registering flanges. The shaft is disposed in the upper housing and extends downwardly inside the power spring, and supports a transport shaft in an opening in its lower end so that the transport shaft has stub ends projecting radially from each side of the shaft extension. A cam roller is rotatably mounted on each of the pair of stub ends, and each roller engages the downwardly facing surface of a hollow annular cam disposed around the shaft extension and above the cam rollers. With such engagement the power spring is compressed between the top surface of the cam and the top closure of the housing, to an appreciable extent in the lowermost position of the cam and to a major extent when the cam is pushed upwardly to its top most position. A striker disposed below the cam and surrounding the lower end of the shaft is secured so the cam to that cam and striker move as a unit. In such arrangement the lower housing supports only the anvil and working tool, and its main function is to hold the working tool so that the upper surface of the working tool is located in a predetermined position relative to the striker.

The safety feature of the invention lies in the addition of a guide ring and a number of members supported by and extending from the guide ring, the guide ring being basically an annular member which is fitted between the two flanges of the upper and lower housings. The guide ring is secured to the upper housing by a pair of diametrically opposed lugs extending inwardly from the flange of the upper housing. At the quarter points between such lugs there are a pair of radial openings in the guide ring, and through such openings extend a pair of studs each of which has a rotatably supported guide bearing on its end. Each guide bearing enters a vertical slot on the outer surface of the striker, and serves to prevent the striker from twisting. The striker slots extend for its complete length and register with a pair of blind grooves 0n the outer surface of the cam member, such blind -to compress the power spring to its lowermost compressed condition by tightening the safety bolts until the guide ring is drawn tight against the flange of the upper housing. No press or vise is necessary to accomplish this assembly operation.

To complete the assembly operaton, it is necessary to exert an upward force on the cam, as further discussed below, so that the transverse opening in the lower end of the main shaft will stand sufficiently clear of the cam surface so that the transport shaft can be inserted and the pair of bearings can be mounted on the ends of the shaft. Once this has been done, the upward force can be released, the striker can be attached to the cam and the lower housing with the working tool it supports can be secured to the upper housing by the series of screws which extend through the registering flanges of the two housings and also through the guide ring sandwiched between the two flanges. In normal operation, the safety bolts play no part because the power spring is held in its partially compressed condition by either the working tool or the anvil.

When the lower housing, together with the working tool and anvil, is removed from the assembly, the principal and ordinary means for preventing the power spring from expanding to its free state is the engagement of the cam rollers with the cam. If either the shaft extension or the transport shaft should be broken so that the cam rollers cannot effectively restrain the power spring, the safety bolts and the guide stud and bearings act together to define a stop for the cam and thus restrain the power spring to its proper position. Gradual and alternate disengagement of the safety bolts will then cause the power spring to expand safely to its free length.

The contribution of the present inventors will be more readily comprehended by reference to the attached drawing, in which:

FIG. 1 is an exploded perspective view of a complete embodiment of the present invention, omitting any Working tool but including the adapter plates 20 used to secure the tool to a working vehicle, e.g., a backhoe of a tractor.

FIG. 2 is a longitudinal section through an assembled version of the same embodiment, the orientation being picked to show the pair of striker guide bearings 13 and the figure being drawn at a time when the cam and striker are just being released after reaching the top of the compression stroke. A working tool 70 has been added in FIG. 2, and the adapter plates 20 shown in FIG. 1 have been omitted.

FIG. 3 is a partial and second longitudinal section of the same impact tool, rotated 90 degrees from the position of FIG. 2 to show the pair of safety bolts 11 securing the safety plate 12 to the upper housing 19. In this figure the striker 9-cam subassembly is shown at the instant of impact with a working tool 70.

FIG. 4 is a perspective view of the same tool with the lower housing and striker removed.

FIG. 5 is a perspective view of cam 15.

FIG. 6 is a perspective view showing assembly or disassembly of the safety ring 12 from the upper housing 19.

OVERALL DESCRIPTION, TOP TO BOTTOM The motive power for the impact tool is preferably supplied by a hydraulic motor 23 having a pair of ports 36 for coupling the motor to a pair of hydraulic hoses connected at the other ends to a hydraulic pump, typically the pump of a tractor having a backhoe mounted on one end to support a series of tools such as a digging bucket or the impact tool of the present invention. Motor 23 has at its lower end an outturned mounting flange 37 through which extend a plurality of cap screws 24 to engage registering threaded openings 38 extending downwardly into the top of upper housing 19. Also projecting from the lower end of motor 23 is its shaft 39 having the longitudinal splines illustrated. For convenience of description, motor 23, motor shaft 39 and the balance of the tool are illustrated and described as having a vertical orientation, but it is to be understood that the entire tool will operate with equal effectiveness with any other orientationhorizontal, inverted to cut into a ceiling, or at various intermediate angles.

Upperhousing 19 consists basically of a large outer sleeve 41, a smaller diameter and shorter inner sleeve 42, and an annular top cap 43 joining and preferably integral with the two sleeve portions, the two sleeves being coaxial and disposed with their common axis vertical. The upper surface of cap 43 is counterbored at 59 around the opening through inner sleeve 42 to provide a seat for thrust bearing race 26, needle thrust bearing 27, and the flanged upper end 46 of shaft extension 22. The lower 4 end of upper housing 19 is open, and is provided with an outturned connection flange 44.

Shaft extension 22 has a central longitudinal opening 47 extending part way down from its upper end, and such opening is provided with longitudinal splines and grooves registering with the splines and grooves of motor shaft 39, so that when the motor turns shaft 39 it also turns shaft 22. The inner sleeve 42 serves as a bearing support for shaft extension 22, and a pair of needle (roller) bearings 18 are pressed into the bore of sleeve 42 from both ends to transmit radial loads and permit free rotation of the shaft extension by motor 23 and its shaft 39, thrust loads being transmitted through bearing 27.

Upper housing 19 is also formed with a pair of diametrically opposed projections 48 formed integrally with its other parts. Each projection presents an outwardly facing surface 29, and each is provided with the indicated plurality of drilled and tapped holes. A pair of adapter plates 20 are provided with a like number of registering openings, and are secured to housing 19 by cap screws 21 threaded into the indicated openings. The pair of upper openings 50 through each plate 20 are designed to secure the impact tool to the dipper stick and bucket control linkage of a backhoe with the aid of bucket pins mounted between opposed openings 50, none of such supporting structure being shown because it is well known and forms no part of the present invention.

Disposed in a transverse opening 40 adjacent the lower end of shaft extension 22 is the transport shaft 28', a member which does not rotate about its own axis but turns only with the shaft extension 22 and extends from each end of transverse opening 40 sufliciently far to support a transport bearing 25 in rotating relationship. The pair of transport bearings 25 simultaneously engage the downwardly facing cam surfaces 52 of the two-cycle cam member 15 and roll over such surfaces during rotation of shaft extension 22 to cause the cam 15 to ride up and down with a longitudinally reciprocating motion.

As particularly shown in FIG. 5, cam member 15 consists of essentially a downwardly extending sleeve 51 having the aforementioned cam surfaces 52 machined on its annular lower and surface, an outwardly extending flange 53, and a tapered sleeve 54 extending upwardly from flange 53, all three parts preferably being made as an integral whole. All three parts of cam 15 receive shaft extension 22 in their axial bores, sleeve 54 having a close fitting bore in its upper end to receive the shaft snugly and being there provided with a lubricant seal 16, e.g., a square section packing ring, to prevent leakage along shaft 22.

Coaxially disposed about shaft 22 between the top 43 of the housing 19 and the flange 53 of cam 15 is the power spring 17. The spring is kept in coaxially aligned position by a snug fit at both of its ends to enlarged portions of other members; inner sleeve 42 of the housing at the top of the spring and upper cam sleeve 54 at the bottom. However, neither end of spring 17 is threaded onto the members it contacts, and each fit is loose enough so that the spring will readily fall away from its supports in the absence of any restraint. In assembly the spring 17 is under some compression at all times, even at the bottom of its power stroke. During the upward or compression stroke of cam 15 the cam rollers 25, which are fixed longitudinally relative to the housing 19, roll on the inclined cam surfaces 52 to push cam 15 upwardly and thus compress spring 17 to a maximum energy storage condition at the high points or shoulders 56 of cam 15, as shown in FIG. 2.

Lower housing 5 has a flange 58 of a size corresponding to that of the flange 44 of upper housing 19, and such flanges are drilled and tapped to receive the circumferential series of cap screws 4 which tightly secure the tWo housings together in end-to-end and coaxial relationship. However, between the two flanges is the striker guide ring 12 of the invention, which also receives the series of cap screws 4. Before the housing halves are secured to each other and guide ring 12, the guide ring is fastened to upper housing 19 by a pair of safety bolts 11 threaded upwardly through appropriate tapped holes in the pair of short lugs 45 (FIGS. 1 and 3) projecting inwardly at the bottom of the housing, at the same axial location as outturned flange 44. These openings are located so that they will be covered by the flange 58 of lower housing 5 when the latter is added, and the openings for safety bolts 11 are accordingly countersunk to receive the heads of bolts 11 and thus permit a flush fit of lower housing 5 and striker guide ring 12, as shown in FIG. 3. This arrangement is designed to prevent removal of the safety bolts 11 prior to removing the lower housing 5, for if this were possible and extremely hazardous situation could be created.

It should also be noted from FIG. 3 that safety bolts 11 are considerably longer than necessary for the purpose of securing guide or safety ring 12 to upper housing 19. This is a safety feature of the present invention to be discussed in more detail below.

Attached to and depending from the flange 53 of cam is striker 9, a member serving the. function of a hammer and making contact through its flat bottom surface 62 with the upper end 71 of the drill bit or other working tool 70. Striker 9 may be thought of as a cup having a very thick bottom wall 61, a sidewall 63- having an internal diameter permitting a snug fit over the depending sleeve 51 of cam 15, and a thick outturned flange 64 of essentially the same inside and outside diameters as flange 53 of the cam member 15. The two flanges 53 and 64 are butted together and secured with a circumferential series of cap screws 8, so that the cam and striker move up and down as a unit. The volume of space 66 defined by the assembly of the two members is the working region for the rapidly moving cam rollers 25, and is filled with a relatively heavy lubricant 67.

It should be noted from FIG. 2 that the thick flange 64 of striker 9 is provided with a pair of vertically extending slots 69 extending inwardly from its outer surface and for the full axial dimension of the flange. In assembly such slots register with a pair of blind slots or pockets 55 in the flange of cam member 15, so that each slot 69 and pocket 55 serves as a path for a guide roller 13 supported on a stud 65 extending inwardly through striker guide ring 12 and secured at its outer end by a nut 14. Since the upper axial limit of the combined slots is defined by the portion of flange 53 left intact when forming pocket 55, such pocket or its bottom wall defines a stop limiting the downward movement of cam 15, striker 9, and power spring 17. This safety aspect of the invention will be further discussed below.

Working tool 70 (see FIGS. 2 and 3) is supported in the reduced diameter lowermost end 76 of lower housing 5 so that its upper or anvil surface 71 is disposed below the working surface 62 of anvil 9. Below such anvil surface of tool 70 is an outwardly projecting flange 72 which is received in a corresponding annular groove 73 of the longitudinally split guide sleeve 3. The groove 73 of guide sleeve 3 has a longer axial dimension than does flange 72 of the tool 70, and in the relative positions shown in FIG. 2 flange 72 is pushed up to the top of groove 73 because the bottom of the tool is in forceful contact with a rock or pavement to be cut.

If the impact tool is raised to lift the working tool out of working contact with such pavement, tool 70 will slip down in housing 5 until its flange 72 contacts the bottom wall of groove 73. This will cause the anvil surface 71 of the working tool to fall to a position lower than the adjacent annular surface 77 of anvil member 6. Operation of the impact tool in such condition (which is not recommended) will cause working surface 62 of striker 9 to contact anvil 6, so that the anvil and housing will absorb the impact energy. The anvil is formed as a heavy ring having the reduced diameter lower portion 78 seating in the corresponding recess in lower housing 5 and held against upward movement by the split retaining ring 7.

Working tool 70 is held in its position of limited slidability with respect to the housing by virtue of its described interfit with tool guide sleeve 3, and sleeve 3 is removably fixed to the housing against all axial movement. This is accomplished at the top of the sleeve by its butting fit against the small inturned flange 75 of lower housing 5, and at the bottom by causing its lower end to butt against a ring spacer 2, which in turn contacts a split retaining ring 1 partially underlying spacer 2 and partially engaging the. indicated annular groove formed in the inner surface of the lower housing 5. To change working tools or bits it is only necessary to engage the split snap ring 1 with the usual snap ring tool to remove the snap ring from the groove in the housing.

OPERATIONfiSIZE While the objects of the invention do not include improvements in the operation of the impact tool, it may be mentioned that the illustrated embodiment has been made in a size having the following characteristics.

Overall length without a working tool-32% inches Overall length with a chisel shaped moil or bit44% inches Maximum cross-sectional dimensionl5 inches Blows per minute at 23 g.p.m.-l,000 Blows per minute at 17 g.p.m.-740 Working pressure8001500 p.s.i. Energy to anvil surface of Working tool125 ft.-lbs. (per blow) Weight without working tool or adapter plates 20245 lbs. Weight with adapter plates 20-275 lbs. Temperature rise of working hydraulic fluid-approx.

F. Time to change over tools mounted on backhoe, impact tool to bucket or vs.approximately 7 min. Nominal working stroke of cam-striker% inch Power spring:

Free length-9% inches Pre-load-2000 lbs. Load at maximum working compression2500 lbs.

SAFETY FEATURESDISASSEMBLY The contributions of the present inventors can perhaps be most easily understood by a description of the methods of disassembling the complete tool for purposes of examination, replacement of worn parts, etc.

The impact tool is disassembled from the bottom upwardly, the working tool 70 (moil point, bit, tamper, or the like) being removed first, together with spacer ring 2 and split guide sleeve 3-by removing the retaining ring 1 with a pair of snap ring pliers. Thereafter lower housing 5 with anvil 6 held in place by snap ring 7, is removed by loosening cap screws 4. The latter should be a relatively simple operation, but if the screws and housing do not loosen and separate readily, the interior parts of the tool may be damaged, indicating the need for caution.

With lower housing 5 removed, the balance of the tool can be best visualized as shown in FIG. 3. The striker 9 is then removed from the cam member 15 by loosening screws 8, taking care not to spill the lubricant lying in the hollow of the striker cup.

At this point the remaining portion of the assembled tool will appear as shown in FIG. 4, the guide ring 12 still being held to upper housing 19 by safety bolts 11 and cam 15 being restrained against downward movement both by the firm seating of cam rollers 25 in the low points or depressions 57 of cam surface 52 and the pair of guide rollers 13 engaging the pockets 55 in cam flange 53, the latter engagement not being complete if the usual tolerances obtain. The mechanic must at this point keep in mind that a highly energized power spring is being held in compression above cam 15, and that cam 15 must continue to hold the spring back until it is gradually unloaded and permitted to return to its natural length.

Before disconnecting any' additional elements it is recommended that a field jig be set up by inverting the lower housing so that its flange 58 rests on a floor or some heavy timbers, as shown in FIG. 6. On this is placed a spring compression tool 33 having a fiat base 79, which should be centered on the small end 76 of housing 5. This tool 33 has a sleeve 81 which is integral with and projects upwardly from its base 79, the sleeve being di mensioned to fit snugly over the depending sleeve 51 of cam with the top edge of sleeve 81 butting against the lower surface of cam flange 53. This sleeve is cut to form a pair of diametrically opposed windows 82 which should be aligned with the cam rollers 25.

Since the cam rollers 25, in the disassembly condition shown in FIG. 4, will be tightly engaged with the cam surface 52, it is necessary to apply some compression to the spring to take the load off the cam rollers so that both the rollers and their supporting cam shaft 28 may be removed. With the tool still supported in a backhoe and the lower housing 5 and compression tool 33 disposed as shown on FIG. 6, this is accomplished by manipulating the boom of the backhoe to lower the boom and the impact tool supported by it. This in effect squeezes the cam 15 and power spring 17 between upper housing 19 and compression tool 33, and causes rollers to stand clear of cam surface 52.

With the spring still held in such compression, a long punch is aligned with one end of transport shaft 28 and it is pushed or driven out of its seat in shaft extension 22, causing rollers 25 to fall clear. Still holding the power spring compressed by pushing down with the backhoe boom against the compression tool 33, the next step is to gradually back off the pair of safety bolts 11. This is most Safely done by unscrewing one bolt 11 an increment of 2 or 3 revolutions, then unscrewing the other bolt 11 the same number of turns, back to the first for an additional increment, and so on until the bolts are both removed and guide ring 12 falls clear together with its pair of guide rollers 13, studs 65 and nuts 14 still in place. Once this has been done, the backhoe boom may be lifted slowly to take all compression out of power spring 17. The spring is removed from the bottom, and motor 23 and shaft 22 are removed from the top after unscrewing the cap screws 24. Substantially the reverse procedure is followed in assembling the tool after it has been cleaned, inspected and furnished with new seals and any necessary replacements.

The above procedure is the one recommended for safe field disassembly, and it is further recommended that a substitute be found for compression tool 33 if the one furnished with the impact tool cannot be located, e.g., a short piece of pipe of appropriate dimensions with the indicated windows formed by a saw or torch (or even use a press, if one happens to be available). However, the present inventors recognized that people will not always follow recommended procedures, and further visualized the possibility of an unusual hazard if the ends of transport shaft 28 should be broken off so that neither of the cam rollers 25 nor the shaft itself would be able to engage cam 15 to prevent power spring 17 from expanding to its free length.

In the event of such breakage during disassembly, the cam will be pushed downwardly by power spring 17 until striker guide bearings 13 are firmly seated in pockets 55 of the cam. In the absence of such guide bearings a highly hazardous condition would exist, as removal of the lower housing 5 would permit power spring 17 to expand and propel cam 15 and attached striker 9 in an unpredictable direction.

Even in such broken-transport-shaft condition, the disassembly procedure recommended is the one outlined above, i.e., using the field jig of FIG. 6. However, for

both this condition and for ordinary disassembly the use of the field jig can be safely omitted by simply unscrewing the pair of safety bolts 11, always alternating from one to the other and unscrewing one only a small increment before switching to the other, and vice versa. The

reason for providing these bolts in an oversize length is to permit full expansion of the power spring to its free length prior to separation of the safety ring 12 from the housing. In assembly this makes it possible to compress the spring without the use of any compression device such as a press.

It is imperative in disassembling the tool without the recommended field jig to keep in mind that transport shaft 28 and cam rollers 25 must be removed before loosening safety bolts 11. If the mechanic who is taking the tool apart should commit the error of leaving the transport shaft and cam rollers in place while he is loosening safety bolts 11, he would of course defeat the purpose of the safety bolts, which is specifically to permit the gradual and safe expansion of the power spring. This error should become apparent to him before he completely removes the safety bolts, from the fact that there is no downward pressure on the safety ring from the power spring, and he can retighten the safety bolts until the transport shaft and bearings are removed.

It is also a part of the undersigned inventiors contribution that guide bearings 13 serve a dual function. In addition to the described safety feature, which may never come into action if there is no breakage and the recommended procedures are followed, they serve the more active function of guiding or restraining the cam and striker to a strictly vertical path of action, or in more general terms to an axial line of motion, free of any rotation. This, of course, is brought about by the interfitting of bearings 13 in the vertical slots of striker 9 and the registering pockets 55 of cam 15. While there is sufficient clearance between the outer surface of each roller 13 and the vertical sides of its operating s ot 69 so that a centered roller makes no contact, in the operation of the tool there is alwys some tendency for the cam-striker to twist, causing the roller to contact and roll against the sides of the slot, thus preventing such twist.

It may also be mentioned that in proper and ordinary operation neither guide rollers 13 nor cam rollers 25 contact the bottom of their slots (depression of cam surface) when the striker hits either the working tool or the anvil. This, of course, prevents any impact force from being delivered to these rollers and thus prolongs their lives.

It should also be mentioned that the free mounting of the power spring combined with the strictly vertical movement of the cam and striker combine to furnish several advantages: (1) torsional stresses in the power spring are kept to a minimum, thus making the total spring stresses more accurately predictable and simplifying its design, (2) the relative motion between the cam rollers and the cam is better and more predictably controlled as the circumferential reciprocating motion that goes with a fixedends power spring and unguided cam is eliminated, avoiding the possibility that the cam rollers can jump from the high shoulder to a spot so high on the rising cam surface at the moment of impact as to damage the rollers, and (3) the very difficult problem of machining seats for the variable pitch ends of the spring is avoided.

We claim:

1. In an impact tool which 'is typicaly vertically oriented to deliver downward vertically blows relative to the earths surface, such impact tool comprising a vertically elongated upper housing having an open lower end, a vertical drive shaft mounted in said housing for rotation relative to said housing and secured against vertical movement relative to the housing, a power coil spring surrounding said shaft and abutting at its upper end a closure on the upper end of the housing, a cam member disposed below said power spring in contact with the lower end thereof and surrounding the lower end of said shaft, said shaft supporting a transport shaft in a transverse opening adjacent its lower end and having at least one end projecting from the transverse opening, and a cam roller mounted on each said projecting end, said cam member having on its lower end a downwardly facing annular cam surface disposed to contact said rollers to alternately compress and release said power spring during rotation of the drive shaft, the improvement comprising a guide ring secured to the lower end of the housing by a number of threaded connection members, at least one guide member supported in the guide ring and projecting radially inwardly to terminate in a downwardly facing peripheral pocket in said cam member, said threaded connection members having a length in excess of that required merely to secure the guide ring to the housing, such length being sufiicient so that, during assembly of the guide ring to the housing and prior to adding the transport shaft and cam roller, the connection members may be tightened to gradually and safely compress the power spring between the housing and the cam member.

2. In a cam-and-spring type impact tool which may have any desired orientation and is typically disposed to deliver downward vertical blows to the upper end of a working tool, such impact tool having a housing with a closed upper end a power shaft mounted in said housing for rotation relative thereto, at least one cam roller supported on a transport shaft extending through a transverse opening at the lower end of the power shaft, a cam member surrounding the power shaft and having a downwardly facing annular cam surface engaged by the cam rollers to reciprocate the cam member between a high position at a drop-off shoulder on the cam surface and a low position at a depression on the cam surface adjacent such drop-off shoulder, a helical power spring surrounding the shaft between the cam member and the closed upper end of the housing, such power spring being partially compressed even in the low position of the cam member and a striker member secured to and depending from the cam member and surrounding the lower end of the power shaft, the improvement comprising a guide ring secured to the lower end of the housing by a number of threaded connectors extending vertically through the ring and into registering and similarly threaded openings in the housing, said guide ring supporting at least one radially projecting guide member terminating inwardly in a longitudinal guide slot in the periphery of the cam-and-stn'ker subassembly having a downwardly opening pocket at its upper end to define a downward stop for movements of the cam-and-striker, said threaded connectors being sufficient- 1y long to compress said power spring during assembly and permit it to expand to its free length during disassembly while it is still engaged with the housing.

3. In an impact tool which includes a housing, a shaft rotatably supported within said housing and typically disposed in a vertical position, a cam and striker mechanism disposed within said housing about said shaft, transport means supported by said shaft and engaging said cam and striker mechanism to reciprocate the mechanism vetrically during rotation of the shaft, and a power spring surrounding the shaft and compressed between the upper end of the housing and the upper end of said mechanism, the improvement comprising a guide ring secured to the lower end of the housing by a plurality of overly long threaded connecting members extending vertically through the guide ring and into threaded holes in said housing, and at least one guide member secured to and extending inwardly from the guide ring and toward the cam-andstriker mechanism to terminate in a slot in the periphery of said mechanism having a blind upper end, said pair of threaded connecting members being of sufficient length so that they may be partially backed off from engagement with the housing to permit full expansion of the power spring to its natural length while the connecting members are still threadedly engaged with the housing.

4. In a machine wherein a power spring is alternately compressed from a condition of lesser compression to a condition of higher compression between a fixed member and a surface of a rotary cam reciprocating up and down coaxially with respect to the power spring, and said power spring is ordinarily prevented from expanding to its free length by cam roller means engaging the cam surface of said cam, a safety feature improvement comprising a safety ring surrounding said rotary cam and secured to said fixed member by a plurality of overly long safety bolts extending through the safety ring and through tapped openings in said fixed member extending coaxially of said spring, and at least one stud member projecting inwardly between the guide ring and the cam so that it is secured to one of them and extends into a slot in the other which terminates in a blind end defining a stop for downward movement of the cam and spring in about the lower compression condition of said spring, said safety bolts having suflicient length to be at least partially engaged with the fixed member when the power spring is expanded to its free length.

References Cited UNITED STATES PATENTS 1,511,566 10/1924 Kollock 1731 19 X 2,556,163 6/1951 Beeson 173--1l9 X 2,741,924 4/1956 Tar water 1731 19 X 3,186,498 6/1965 Roll l73123 3,302,732 2/1967 Roll 173-123 3,426,856 2/ 1969 Roll 173-119 NILE C. BYERS, 111., Primary Examiner 

